| Animal population sizes vary temporally and spatially. Documenting or testing for patterns in empirical data is one approach that may facilitate our understanding of population fluctuations. My work attempts to better understand population variability through detection of patterns.; First, the frequency and severity of catastrophic events may be important to the persistence of populations. My re-analysis of previous work suggests that catastrophic declines are in fact much less common than suggested. I believe that current data supports the elimination of the distinction between environmental stochasticity and catastrophes, and that catastrophes represent the tail of environmental stochasticity distributions.; Second, my results indicate that delayed density-dependent feedbacks characterizing extrinsic regulation (e.g., trophic-level interactions) are common in both small and large mammals. However, the effect of such delayed feedbacks on the variability in population growth rates differed with body size. Large mammals showed less variance and more stable dynamics than small mammals. Patterns of population dynamics in small versus large mammals contradicted previous hypotheses.; Third, I investigated the dynamic properties of cyclical populations of Canadian muskrats. Cycle length varied between three and 13 years, with three to five year periods located in subarctic/arctic ecozones. I hypothesize that the 4-year cycles result from predation by red fox, which exhibit 4-year cycles in arctic regions. Remaining ecozones averaged eight to nine year cycles. However, the relative contributions of direct and delayed density-dependence varied. I hypothesize that shifts in the nature of mink predation are responsible for the changes in the relative contribution of direct and delayed density-dependence.; As a follow-up, I investigated the spatial attributes of mink and muskrat interactions in Canada. In western Canada, trophic interactions appear strong, and mink cycles lag behind muskrats 2–3 years. In central Canada, mink lagged behind muskrats 1 year, and trophic interactions were mostly intermediate. In eastern Canada, trophic interactions appeared weakest, with no distinct time lags. Stronger interactions in western Canada may be a result of decreased prey diversity, forcing mink to specialize more on muskrats, whereas comparatively stronger perturbations stemming from other trophic interactions may alter the estimated interaction between mink and muskrat in eastern Canada. |
